1. Field of the Invention
The present invention relates to a method of traffic quality evaluation and traffic measurements in packet network and asynchronous transfer mode network. Traffic quality evaluation is utilized primarily for traffic design and confirmation of quality of service evaluation after the system has been constructed. Traffic quality evaluation apparatus observes packets that have been duplicated from the packets passing an attention point between switching systems, and determines arrival time of packet itself or a specific cell contained in the packet, thereby estimating the arrival time of packet or cells contained in the packet as well as loss ratio of cells.
This application is based on patent application No. Hei 10-68772, No. Hei 10-264769 and No. Hei 10-267076 filed in Japan, the contents of which are incorporated herein by reference.
2. Description of the Related Art
In information communication systems, variations in the quality of service such as delays and data loss are produced depending on the traffic intensity. Therefore, to construct an economic and high performance information communication system, quantitative understanding of the relationship between the traffic intensity and the quality performance under a given set of conditions of operating environment, such as buffer size and circuit speed, CPU power, memory and the like, become essential so that an appropriate size of buffer memories, for example, can be provided for optimum performance of the network.
To achieve this end objective, two basic methodologies have been used. The first method is based on simulation. A logic to simulate a target system is assembled into a computer. The computer is then input with statistically processed results obtained from traffic measurement in the actual network system, and traffic based on the results of processing is simulated by generating random numbers, and the resulting quality for the generated traffic is evaluated.
The second method is based on evaluating a mathematical relationship between quality and operating environment such as traffic buffer size obtained by traffic theory. Traffic conditions are derived from statistical processing of traffic measurement in the information network system, as in the first method, or the person evaluating the system selects suitable traffic conditions under certain assumptions. In either method, the evaluation approach is based summarizing the measured results once into a small number of statistics, and analyzing the summarized statistics.
However, these conventional methods present the following problems in providing a quality of service (QoS) evaluation to perform accurate traffic design for a given network.
(1) Traffic measurements in information communication systems lose a lot of information related to the traffic, because of many restrictions in measurement items pre-provided in the system, such as measurement duration.
(2) Much information is lost by statistically summarizing the measured traffic results into a small number of prearranged statistical parameters to fit certain probability/statistical model. Actual traffic activities are far more complex than those that can be described by a few parameters of probability/statistical models. Consequently, errors introduced by modeling are such that they cannot be ignored.
Furthermore, traffic measurement techniques are important in contributing significantly to design an economical highspeed network. Methodology for measuring network traffic can be divided into two broad categories: one utilizes devices within the network such as end systems, switches and routers; while the other utilizes external measuring devices. In either case, items to be measured are determined by the devices or softwares provided in the switches and externally attached traffic measuring devices. It is true that some flexibility in choice can be provided when measuring the traffic by application programs in end systems, because they allow modifications to be made to the programs, In such cases, however, it is important to remember that what is being measured is not the traffic within the network, but the traffic that the relevant end system is transmitting and receiving.
Internet and ATM networks are realizing not only monolithic tasks such as voice transmission but a variety of information transmission tasks. Thus, to achieve an effective use of the network capability, it is necessary that the network operators come to clear understanding of the variety of traffic conditions that may exist in the network. However, because the existing measurement devices can provide only fixed traffic items for measurements, it is difficult to perform traffic measurements within a network in a variety of conditions, without exhaustively seeking out all combinations of a variety of traffic measurement conditions. However, it is impossible in practice to respond to all such combinations, considering the limited nature of the processor capability and memory capacity in a given measuring system in existing communication networks.
The present invention related to the quality of service evaluation has been developed in consideration of the background described above, and an object is to provide an evaluation apparatus to enable traffic measurements without loss of traffic information. Also, another object of the present invention is to provide an evaluation apparatus that enables to evaluate the quality of service without being affected by the modeling.
The object related to the quality of service evaluation has been achieved by the following features disclosed in the present invention.
(1) Raw traffic data are obtained by inserting a splitting device or by using accessing history. Traffic measurement items provided in a communication system are not used.
(2) Raw data obtained are directly input into a simulation model without summarizing into pre-arranged statistical parameters. As a result, near real-time traffic is reproduced. To perform such a simulation continually, the measuring point and the execution section for the simulation logic are connected on-line.
(3) QoS evaluation is performed by simulation and numerical equations are not used.
Specifically, the present QoS evaluation apparatus is provided with means for splitting and accepting the packets passing through an attention point in a switching system, and evaluates the quality of service dependent on by observing the packets splitted off from the network.
The features provided for the present quality of service evaluation apparatus are:
means for accepting a packet passing through an attention point in a switching system and duplicated and splitted at a splitter, and assigning a timestamp to a specific processing unit included in said packet;
means for estimating arrival times of processing units included in said packet at said attention point on a basis of said timestamp for said specific processing unit given by said arrival detection section; and
means for simulating arrival time of said packet and processing discipline at said attention point which arrival time to correspond to an estimated arrival time of said packet at said attention point obtained by said estimating section, according to a pre-determined simulation logic.
The switching system is an ATM switching system, and said attention point may be an output-line buffer in said ATM switching system, then said processing unit is a cell and said specific processing unit can be the first cell in an object packet. Or, said processing unit may be a cell, and said specific processing can be an individual cell in an object packet.
In this case, the estimating section may include means for estimating an arrival time of an (i)th cell in said packet according to a relation:
[a timestamp of said first cell+(ixe2x88x921)xc3x97(cell length/input-line speed)], or
an estimated arrival time of an (i)th cell comprising said packet may be calculated from a relation:
[an estimated arrival time of said first cell+(ixe2x88x921)xc3x97(cell length/input-line speed)],
where said estimated arrival time of said first cell is given by a sum of a base time Txe2x80x2 and an estimated value of a time interval required for cells that output from a switching system between a reference time and a timestamp of said first cell to arrive at said attention point.
When cells output from a switching system without creating an idle interval between the first cell of a receding packet and the first cell of said object packet, then said base time is equal to an estimated arrival time of the first cell of the preceding packet, and said reference time is equal to a timestamp of the first cell of the preceding packet; and
when there is an idle interval between the first cell of a preceding packet and the first cell of said object packet, then said base time is equal to a reference time, which indicates a time when a most recent idle interval becomes non-idle.
Or, the estimating means is provided with a table that records estimated cell arrival rates at each instant of time, and is provided with a computing section to read out an estimated value xe2x80x9caxe2x80x9d corresponding to a time indicated by a timestamp of a packet, and
if xe2x80x9caxe2x80x9dxe2x89xa71, an estimated arrival time t(l) for the first cell of an object packet is calculated from a relation: [ail estimated arrival time txe2x80x2(1) of the first cell of a preceding packet]+[(the object packet timestamp t)xe2x88x92(a preceding packet timestamp txe2x80x2)]/(estimated cell arrival rate xe2x80x9caxe2x80x9d); and if xe2x80x9caxe2x80x9d less than 1, an estimated arrival time t(1) for the first cell of an object packet is calculated from a relation: (an arrival time of the first cell of the object packet)+(a waiting time of the first cell of the object packet)=the transmitting time of the first cell of the object packet=a timestamp t of the object packet.
Also, said switching system is a router and said attention point may be a router output-line, then said processing unit is a packet, and said estimating section includes a processing section to calculate an estimated arrival time for an (i+1)th packet so that:
when the completion time of the (i) the packet transmission is followed continually with the starting time of the (i+1) th packet transmission, a relation is used such that: [(i)th packet estimated arrival time+the starting time of the (i+1) th packet transmission]/2, where said the starting time of the (i+1) th packet transmission is obtained by subtracting a value of (packet length of (i+1)th packet)/(output-line speed) from an arrival time of (i+1)th packet; and
when the completion time of the (i) the packet transmission is not followed continually with the starting time of the (i+1) th packet transmission, a relation is used such that: (i)th packet estimated arrival time=the starting time of the (i+1) th packet transmission, where said the starting time of the (i+1) th packet transmission is obtained by subtracting a value of (packet length of (i+1)th packet)/(output-line speed) from an arrival time of (i+1)th packet.
Accordingly, QoS evaluation may be performed without suffering loss of traffic information, and without being affected by the effects of errors introduced by modeling. Further, the evaluation process may be carried out without resorting to approximating equations.
An object for the invention related to traffic measurements is to provide a traffic measuring methodology that is flexible to enable to customize traffic measurement items for individual cases of traffic in various communication modes.
The object is achieved by using a traffic measuring apparatus comprising:
a low level layer processing section for performing protocol processing in functional layers including a protocol layer residing immediately below an attention protocol layer in a network for transferring information using a specific processing unit;
an object condition discrimination section for deciding whether or not measurement conditions specified by an application programming interface, known as an API, are satisfied in a data unit that has been subjected to processing in said low level layer processing section; and
an operation section for carrying out measuring actions specified by said API for a data unit that has been judged to satisfy said measurement conditions; and
an application section for computing desired contents of traffic measurement by manipulating raw data output from said operation section.
It is preferable that the above API is an upper level API that determines parameters for an object to be measured, measurement items and measurement methods, in terms of user-friendly terms such as addresses or protocol types in each protocol layer, protocol data units in each protocol layer.
In this case, the traffic measuring apparatus is further provided with an API conversion section for converting upper level APIs that determine user-friendly parameters to a general purpose API for purposes of taking traffic measurements. In this case, said object condition discrimination section and said operation section use said general purpose API in place of said upper level APIs.
Also, it is preferable that an API used by said operation section is a logic equation based on bit values and time information contained in data units.
Accordingly, one evaluation apparatus is able to provide traffic measurements that can be customized to the needs of individual cases of various communication modes.